This invention relates to decorative sheets used for obtaining decorative materials (the term "decorative articles" is intended herein to include articles which constitute parts of buildings such as decorative walls, decorative ceilings and decorative floors as well as individual decorative articles) by imparting desired patterns of surface depressions and protuberances or concavities and convexities (hereinafter referred to as surface "unevenness") to the surfaces of water-containing plastic materials such as cement, mortar and various plaster materials, as well as to processes for producing decorative articles by using the decorative sheets.
In the production of decorative articles by imparting unevenness patterns on surfaces of water-containing plastic materials, a method which uses molds such as a form, template and embossing roller has been chiefly employed. This method of using molds has the advantage of being able to impart unevenness patterns faithfully but at the same time possesses drawbacks in that the molds used are costly, give rise to poor work efficiency, and often require complicated accessory equipment and work.
As a result of various studies directed toward a simple method of forming any desired unevenness pattern, a research group to which we belong found that, by utilizing the characteristic of various resin sheets and the like of deforming by expansion or construction, chiefly by expansion, when they contact a liquid having affinity therefor, by providing, on a sheet of this character, regions which are not subject to the effect of such a liquid or regions differing in the degree in which they are affected by the liquid, for example, by printing and causing the sheet to contact a decorative material layer containing an ingredient which gives rise to expansion deformation in the sheet, an unevenness pattern corresponding to the printed pattern is imparted to the decorative material layer. On the basis of this discovery, the research group developed a process for producing decorative articles, as disclosed in the specification of Japanese Patent Laid-open No. 91061/1977.
More specifically, this process for producing decorative articles comprises the steps of superposing on a decorative layer prior to treatment a sheet provided with regions subject to expansion deformation and regions not subject to expansion deformation due to ingredients constituting the decorative layer, and/or regions having differences of degree of susceptibility to deformation, and then carrying out an appropriate after-treatment, depending on the ingredients constituting the decorative layer, thereby to cause the formation, on the decorative layer, of unevenness corresponding to the various regions. With the above process, by using a hydrophilic deformative sheet, decorative articles having surface unevenness patterns can be obtained from water-containing plastic materials.
It was found, however, that the above process had several problems. For instance, in the unevenness patterns obtained by the above process, waviness appears even on regions of decorative articles which correspond to regions of sheets not subject to expansion deformation and theoretically should be formed flatly, and distinction between uneven regions and theoretically flat regions on the decorative articles, namely, visual clearness of unevenness patterns is reduced. This problem can be solved by applying a pressure to the decorative layers and sheets at the time of expansion deformation of the sheets, as disclosed in U.S. Pat. No. 4,310,370. However, such a pressure application may sometimes be not easy depending upon where the decorative materials are applied, as in the case where unevenness patterns are imparted to wall materials. Also, in connection with the use of hydrophilic deformative sheets in the above process, there exist problems such as (a) sheet deformation occurring during storage, (b) difficulty in peeling-off of sheets from hardened decorative materials, and (c) sheet deformation occurring immediately after contact with water-containing plastic materials which does not permit time required for positioning, adjustment, deaeration, etc. Further, water absorption of sheets from water-containing plastic materials which is necessary for the sheets to deform may cause the plastic materials to lose plasticity, whereby formation of desired unevenness patterns on the plastic materials cannot be accomplished.